U.S. Pat. No. 5,034,394 to Daluge discusses 6-substituted purine carbocyclic nucleosides of the general formula ##STR3## wherein R.sub.3 represents hydrogen or C.sub.1-6 alkyl; R.sub.6 represents C.sub.3-8 cycloalkyl, and R.sub.7 represents a hydrogen atom or branched or straight chain C.sub.1-6 alkyl; or a pharmaceutically acceptable ester or pharmaceutically acceptable salt thereof. Particularly preferred compounds of the Daluge '394 invention include (-)cis-4-[2-amino-6-(cyclopropylamino-9H-purin-9-yl]-2-cyclopentene-1-meth anol and (-)cis-4-[2-amino-6-(cyclopropylmethylamino-9H-purin-9-yl]-2-cyclopentene- 1-methanol or racemic or partially resolved enantiomers thereof.
European Patent Application No. EP 0 434 450 A2 to Daluge discusses enantiomeric compounds of the general formula ##STR4## wherein R represents a cyclopropylamino or N-cyclopropyl-N-methylamino group, and A represents the 2-cyclopentene-1-methanol-4-yl group in either the (1S,4R) or (1R,4S) configuration and their derivatives, with compounds and their derivatives each being in the form of an enantiomer substantially free of the corresponding enantiomer.
PCT Application No. WO 92/18444 to Evans et al. discloses enantiomers of cyclopentene given as the following formulae: ##STR5## wherein X (at the one 1-position) represents hydrogen or an acyl group, and Y (on the CH.sub.2 OY group at either the 4- or 5-position) represents hydrogen or a group that can be readily replaced by hydrogen, optionally substituted by non-interfering substituents. The compounds may be made by biocatalyst-mediated esterification of the racemic secondary alcohols, or deesterification of acyl derivatives or the racemic alcohols. These compounds are useful in the preparation of optionally-protected carbocyclic nucleosides, wherein a heterocyclic base is reacted with an enantiomer IIIa or IIIb by displacement of an acycloxy group. Alternatively, the protected carbocyclic nucleosides may be prepared by reacting a heterocyclic base with enantiomer IVa or IVb, wherein OX is a strong leaving group, via direct S.sub.N 2 displacement.